Procedures are being developed for use of 15N and 13C for structural analysis in solution by nuclear magnetic resonance spectroscopy. The procedures are nondestructive and applicable to mixtures of compounds. The major objective of development of equipment of greater detection sensitivity which permits routine nmr studies of 15N at its low natural-abundance level has been achieved and useful spectra have been obtained of alkaloids, peptides, enzymes, amino sugars, protamines, nucleotides, nucleosides and t-RNA.